Bioprocessing of food industry surplus to obtain novel food ingredients enriched in bioactive peptides

• Food by-products were converted into peptide-rich functional ingredients. • Enzymatic hydrolysis was most effective for brewers’ spent grain, bread, and okara. • Peptides with antioxidant and antihypertensive activities were generated. • Short, proline-rich peptides, stable to heat and digestion, were identified. • A prototype granola with treated residues retained bioactivity and sensory appeal. The food processing industries are responsible for the generation of substantial quantities of protein-rich waste and by-products posing significant environmental and economic challenges. However, their valorization through enzymatic hydrolysis, to produce biologically active peptides, offers a sustainable, circular approach with potential applications in novel functional foods. In this study, aiming at releasing bioactive peptides, several food grade carbohydrases and proteases, alone or in combination, were used to treat brewers' spent grain (BSG), wasted bread (WB), soy okara (SOK), grape pomace (GP), and wine lees (WL). The results demonstrated that, due to their strong endopeptidase activity, Alcalase® and Neutrase® significantly enhanced peptide content in BSG, WB, and SOK, with increases reaching up to 22-fold, while Veron PS exhibited comparatively weaker effects. The radical scavenging activity markedly improved, particularly in WB after treatment with Alcalase® (up to 150 %). Whereas other residues were found to have higher (up to +20 %) antihypertensive activity compared to untreated samples. UHPLC/HR-MS 2 in conjunction with in silico tools led to the identification of numerous peptide sequences that possess significant antioxidant and antihypertensive properties. Moreover, short epitopes (e.g., PFP, PPP, PLL, GLFL), typical of bioactive peptides, were recurrently identified. As proof-of-concept, the enzymatically treated ingredients exhibiting the highest bioactivity were incorporated into a novel functional food prototype, a “granola”, with a nutritionally relevant profile, rich in fibres and protein, and potential multi-faceted health benefits, since the antioxidant and ACE-inhibitory properties were retained after baking.